Event handling changes

The component event function earlier stored as string property but from 0.5.0 version this feature changed to lua_CFunction.
But be careful with the new feature be sure the function was defined before referenced!

~~~~~~~~~~~~
require "vcl"

form = VCL.Form()
form._ = {
caption="Event Test", onClick=function(s) VCL.ShowMessage(s.name) end
}

form:ShowModal()